Just like Amazon, ShopRunner charges $79 annually, and has a free 30-day trial period (after which, you’re charged the $79). But ShopRunner offers free returns, which Amazon does not, eliminating one of the concerns and annoyances of online shopping.

Let’s think about what these services do, and whether they’re a good deal. I don’t know about you, but my family tends to need things in one of two time frames: right away (meaning somebody has to head out to the store like, right now), or in the foreseeable future for birthday presents, Christmas, and such (meaning an order sent with free or very cheap one-week shipping should be no problem, provided we’re on the ball). In either case, I don’t see much reason to need two-day shipping—especially if it’s going to cost me $79 a year. Sure, it’s nice to order something and have it arrive on your doorstep within a couple days, but do you need two-day shipping?

What’s more, while it’s impossible to swing by a physical Amazon store (um, they don’t exist), most people I know tend to drive past stores like Babies R Us and Radio Shack on a daily basis.

Let’s also think about what kind of consumer behavior is likely once you’ve paid your $79 for the service. Naturally, you’re inclined to want to get the most for your money—which in this case would mean placing all sorts of online orders. As the WSJ writes:

Membership in such program acts as golden handcuffs: After prepaying for shipping, members become valuable repeat customers, in order to get the most out of the fee.

Not only are you more likely to order often, you’re also more likely to not bother shopping around to see if competitors have better prices—because again, you already know you have free two-day shipping with the program you’ve paid for, and you’d probably have to pay for shipping from the competitor. (That assumption might not be true, by the way. Check out FreeShipping.org for free-shipping offers and codes.)

Basically, once you’ve paid your membership fee, you’ll probably become a lazier shopper: Chances are, you’ll shop around less, you won’t plan ahead for purchases you know are coming up, and it’ll be easier to justify unplanned impulse buys you stumbled upon while browsing online. Even ShopRunner’s free-returns policy, which sounds as customer-friendly as it gets, effectively helps the consumer turn off his or her brain while shopping. The thinking (or lack thereof) goes: Hey, I can always return this, no sweat and no harm done. So why not buy it?

Why? Because you might just be a lazy shopper—too lazy to even return something that doesn’t fit, or that you’ve figured after the fact that you really don’t need.

I can understand wanting to avoid shopping in brick-and-mortar stores, and wanting to not have to plan ahead and think all the time about getting the best deal. But if you turn off your brain and begin shopping lazily on autopilot, you’ll wind up paying in more ways than one.